Aseismic creep and gravitational sliding on the lower eastern flank of Mt. Etna: Insights from the 2002 and 2022 fault rupture events between Santa Venerina and Santa Tecla

Fault creep along the lower eastern flank of Mt. Etna volcano has been documented since the end of the 19th century and significantly contributes to the surface faulting hazard in the area. On 29 October 2002, during a seismic swarm related to dyke intrusions, two earthquakes caused extensive damage and surface faulting in an area between the Santa Venerina and Santa Tecla villages. On the same day after the two earthquakes, an episodic aseismic creep occurred along the Scalo Pennisi Fault close to the Santa Tecla coastline. On 8 February 2022, during another aseismic creep event along the Scalo Pennisi Fault, we observed the reopening of the pre-existing 2002 ground ruptures mostly as pure dilational fractures. We mapped the 2002 and 2022 surface ruptures, and collected data on displacement, length, and pattern of ground breaks. Ground ruptures affected structures located along the activated fault segments, including roads, walls and buildings. The 2002 surface faulting propagation can be ascribed to a sliding of the Mt. Etna eastern flank toward the SE, as also suggested by the related shallow seismicity, and InSAR and geodetic data between 2002 and 2005. For the 2022 event, differential InSAR data, acquired in both descending and ascending views, allowed us to decompose Line of Sight (LOS) displacement into horizontal and vertical components. We detect a ~ 700 m long and ~ 500 m wide deformation zone with a downward and eastward motion (max displacement ~1,5 cm) consistent with a normal fault. We inverted the InSAR-detected surface deformation using a uniform-slip fault model and obtained a shallow detachment for the causative fault, located at ~300 m depth, within the volcanic pile. This is the first in-depth study along the Scalo Pennisi Fault to suggest a shallow faulting that accommodates Mt. Etna E flank gravitational sliding.